The effect of high pressure homogenization on emulsions containing oat β-glucan : a study of viscosity, stability and molecular weight

Abstract

This master thesis project has been conducted in cooperation with Lantmännen AB who are producers of PromOat® - an oat β-glucan powder concentrate. The main objective of this thesis was to investigate the properties of emulsions containing PromOat® oat β-glucan, focusing on the viscosity, stability, and molecular weight before and after high pressure homogenization (HPH) at pressures of 100, 150 and 200 bars.
The viscosity of emulsions was measured on a shear rate range from 0.1 to 100/s and extrapolated to zero shear force. Results showed a significant decrease in viscosity with HPH and its increasing pressures in both research and control samples, indicating its disruptive character on β-glucan aggregates.
Stability analysis of oat β-glucan emulsions through backscattering measurements indicated no significant differences among the research samples, suggesting that HPH did not affect the overall stability of the emulsions. Obtained results in light of documented loss of viscosity with HPH suggest stabilizing effect of oil droplet size reduction. Control samples showed variations in backscattering behavior, indicating the influence of HPH on stability. Light microscopy images revealed smaller oil droplet sizes in emulsions subjected to HPH pressures, confirming its well documented disruptive effect on oil droplets.
Asymmetrical flow field-flow fractionation (AF4) analysis of oat β-glucan samples using multi-angle light scattering (MALS) and differential refractive index (dRI) detectors showed an increase in average molar mass and average root-meansquare radius with higher HPH pressures, suggesting that re-aggregation of oat β-glucan had occurred under different circumstances than in non-homogenized sample which manifests itself in increased average molar mass and root-meansquare radius.
In conclusion, HPH was found to significantly decrease the viscosity and disrupt the aggregate structure of oat β-glucan in emulsions. The overall stability of the emulsions was not significantly affected. The molecular properties of βglucan, such as molar mass and root-mean-square radius, were influenced by HPH treatment. These findings may contribute to a better understanding of the HPH impact on oat β-glucan properties in emulsions.

Popular Abstract

Picture this - a creamy salad dressing or a velvety mayonnaise. Emulsions like these rely on the delicate balance between immiscible liquids, such as oil and water, held together by a stabilizing agent. The emulsion stability is often enhanced by high pressure homogenization which makes oil droplets very small. Smaller droplets travel slower to the top and delay creaming which means more stable emulsion. Oat β-glucan, a natural polysaccharide found in oats has great potential as a stabilizer through enhancing viscosity and slowing down creaming. Additionally it provides considerable health benefits to the product! To establish the effect of high pressure homogenization on the stabilizing properties of oat β-glucan this project was conducted.
Viscosity is an important property that affects not only the stability but also the flow and texture of emulsion. Through this research it was found that high-pressure homogenization significantly reduced the viscosity of oat β-glucan emulsions. The higher the homogenization pressure (100, 200, 300 bar) the bigger decrease in viscosity. The same thing was observed in water dispersions of β-glucan, suggesting that the viscosity reduction is directly related to the β-glucan.
Emulsion stability was examined using backscattering measurements and light microscopy. The backscattering behavior did not change significantly before and after homogenization, showing that the emulsions stability was not affected by the processing. Microscopic images showed a decrease of oil droplet size after high pressure homogenization. Keeping in mind the viscosity loss mentioned earlier which reduces the stability, joined effect of high pressure homogenization on oat β-glucan and oil did not affect the emulsions’ stability.
The molecular weight of β-glucan was analyzed using asymmetric flow field-flow fractionation. Through this research it was found that higher homogenization pressures led to an increase in the average molar mass of β-glucan. This could mean that products can be better for your health after high pressure homogenisation than beforehand as higher molar mass oat β-glucan is associated with its famous health benefits!
Overall, this research findings give valuable insights into the behavior and properties of oat β-glucan emulsions. Although emulsion viscosity was lost, the overall stability was not affected, even more – health benefits of oat β-glucan were potentially improved through high pressure homogenization! With further exploration, these findings may pave the way for the development of healthier, more stable and delicious food products.

• author: Kiesling, Dominika
• supervisor: Lars Nilsson
• organization: Food Technology and Nutrition (M.Sc.)
• course: KLGM01 20231
• year: 2023
• type: H2 - Master's Degree (Two Years)
• subject: Agriculture and Food Sciences
• keywords: oat, β-glucan, high pressure homogenization, emulsion, stability, food technology
• language: English
• id: 9126134
• date added to LUP: 2023-06-19 12:34:56
• date last changed: 2023-06-19 12:34:56